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feat(js): add Python and TypeScript runtime host functions - #2740
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…2776) `runtime-functions.ts` arrived in #2740 without being added to tsconfig's `include`. tsc compiles a reachable import regardless, so it kept emitting `runtime-functions.js` and every local build and `js.yml` run stayed green. Two things broke on that omission. `publish-js.yml` ships a `js-stubs` artifact whose file list is maintained by hand from `include`, so it never gained the file; the test jobs download that artifact instead of running tsc. And `scripts/tests/test_js_publish_files.py`, the guard added after 0.18.2 shipped without `langchain.js`, reads its notion of "tsc output" out of the same `include` -- so the guard was blind to exactly the file missing from it. v0.20.0 therefore published to crates.io and PyPI while all fifteen `Publish JS` test jobs failed on `ERR_MODULE_NOT_FOUND` for runtime-functions.js, which `wrapper.js` (the package `main`) imports on its first line. `release-js` is gated on those jobs, so npm was never reached and both npm packages remain on 0.19.0. Fixes the omission in both tsconfigs, adds the two outputs to the artifact, and closes the guard's blind spot by checking `include` against the sources on disk. Reproduced the failure locally and verified the fix; 181/181 script tests pass, identical tsc error set before and after, all 34 checks green. Does not republish 0.20.0: only a `refs/tags/vX.Y.Z` ref publishes as npm `latest`, so npm needs a patch release. `Publish Web` failed separately on an npm 404 for `@everruns/bashkit-wasm`, which needs an `NPM_TOKEN` rotation. Claude-Session: https://claude.ai/code/session_01RE65s6DTUE7LzZgc1o6Hzi
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What changed
Node/Bun/Deno applications can register synchronous or asynchronous host functions for embedded Python and TypeScript on Bash, BashTool, and all JavaScript agent adapters. Each execution preserves its caller's AsyncLocalStorage context and supplies an AbortSignal for host I/O. Reset preserves handlers; snapshot restoration accepts fresh callbacks.
Blocking instance access rejects active asynchronous execution, preventing event-loop deadlocks involving host functions, streaming output, and live filesystem handles. Added bounded JSON conversion and explicit callback rows to the capability parity contract; Rust BashTool gains the Python callback builder counterpart.
Why
Extend the shipped Python integration to the native JavaScript SDK and make cross-surface callback gaps explicit. Browser/WASM and C follow in separate PRs.
Before / After
Before: externalFunctions had no callable JavaScript dispatcher; TypeScript runtime options were unavailable. LangChain used synchronous execution internally.
After: Python lookup(21, multiplier=2) and TypeScript await double(21) return 42 through real host callbacks. Local verification: 656 AVA tests and 167 runtime compatibility tests pass, including HTTP request contexts, queued requests, cancellation, timeout/reuse, snapshots, recursive access, worker-thread environments and all agent adapters. A subprocess regression terminates workers with pending or CPU-bound host functions and verifies quiet native teardown; completed ScriptedTool worker shutdown is also covered. Shared JSON codec and Rust tool callback tests pass. CI adds targeted macOS/Windows callback coverage alongside the existing Linux Node/Bun/Deno matrix.
just pre-pr,just test, all-target/all-feature Clippy and the parallel execution benchmark pass locally.Risk
Medium: native callback lifetime and synchronization. Execution-local revocation, weak NAPI dispatchers, bounded queues and blocking-entry guards cover shutdown/cancellation/reentry. Host I/O must observe its signal; application side effects cannot be rolled back.
Checklist